There are many different forms of centrifuge. Thus, DE 14 10 967 A1 describes a drum which rotates about a vertical axis in a cylindrical container for use especially in washing machines. The laundry drum is emptied after each washing process and is then refilled in order to accomplish a new washing process. This centrifuge is thus operated in batch mode. The container with the laundry drum is suspended in a fixed housing which rests on the ground. In order to prevent the container from rotating, several strips project downwardly into several corresponding anti-rotation means which also produce a damping effect upon the vibrations produced by the rotating laundry drum.
From U.S. Pat. No. 4,022,375, there is known a laboratory centrifuge in which an arm having a plurality of test tubes affixed thereto circulates at high speeds of 4,000 to 12,000 revolutions per minute about a vertical axis in a cylindrical protective cover. After a centrifuging process, the test tubes are exchanged; this centrifuge is thus driven in a batch operational, mode. The laboratory centrifuge comprises a drive motor. The drive motor and the protective cover are mounted on a common platform which rests on resilient elements in a housing.
Centrifuges operating in a batch mode are unsuitable for numerous processes in which continuous operation is necessary or at least desired, perhaps with a view to maintaining a continuous supply of the raw materials that are to be treated in the centrifuge or for the continuous further processing of the intermediate products delivered by the centrifuge. On the other hand, continuous operation imposes completely different boundary constraints compared with a batch operation. Thus, vibrations occurring in a batch operation automatically come to a complete stop when the load is changed. They thus only have to be damped on a temporary basis, whereas in the case of a continuous centrifuge operation the vibrations occur permanently and consequently they must constantly be taken into consideration. In consequence, the damping concepts utilised in a batch operation process cannot be simply transferred over.
Other forms of centrifuge are known from GB 2 115 319 A for example. Liquids are processed in this centrifuge in which a motor is arranged above the centrifuge and is damped below relative to the centrifuge by means of shock-absorbent mounts. Such a centrifuge is not intended nor is it suitable for centrifuging sugar massecuites.
Continuously operating centrifuges such as are known from EP 0 487 780 B1 and EP 0 733 406 B1 for instance are used in the sugar industry. Such types of centrifuge, which are also referred to as sugar centrifuges or in the case of continuously operating centrifuges by the catch words continuous centrifuges, can be employed in the cane sugar and sugar beet industries as well as in sugar refineries. They serve to mix, to distribute and to accelerate the sugar massecuites being supplied thereto and thereby free them from foreign entities such as by means of a washing process involving the addition of water or steam.
The centrifuges stand on a suitably firm base in the factory buildings. The centrifuge drums rotate at very high speeds in order to enable them to cope with their task. To this end in particular, they are driven by a drive unit incorporating a motor utilising an endless drive means. The centrifuge drums rotate about a vertical axis and, as a rule, have an upwardly flaring conical sieve basket which forms a discharge edge.
The centrifuge drum has a mounting means. Since the vibrations of the centrifuge drum are not insignificant due to the unavoidable imbalances which occur at the high rotational speeds involved, these vibrations must not to be passed on to the environment. A means for damping the vibration of the centrifuge drum with respect to its environment is thus desired.
It is known to place the complete centrifuge together with its outer housing on vibration damping mounts, namely, on three or more elastomers.
This has the disadvantage that the entire housing is still subjected to oscillatory forces and is prone to vibrate. It is of course the case that, due to the resilient vibration damping mountings between the base and the housing, these vibrations are not transferred to the base—or are merely damped in the transfer process, but on the other hand, the correspondingly vibrating and moving outer housing of the centrifuge imposes permanent and continuous acoustic and mechanical burden on the environment, the latter difficulty also applying for the various connections since both the electrical connectors and the input leads and the supply elements are either mechanically loaded insofar as they are connected to the outer housing or else materials cannot be supplied and removed in a reliable or constantly adequate manner or the lines that are utilised for this purpose cannot be fed-in close to the centrifuge due to the movements of the elements with respect to one another.
In another state of the art, the centrifuge drum itself is mounted inside the housing in a manner such that it is vibration damped with respect to the directly adjacent parts. The problems which ensue in the case where the entire centrifuge including the outer housing is mounted in vibration-isolating manner can then indeed be avoided, but against that, the maintenance of such a conception wherein she vibration-damping mounting is merely in respect of the centrifuge drum is problematic. The vibration damping elements are now located in certain locations in the interior of a complicated assembly so which it is difficult to gain access and they can then only be maintained by specialists. Hereby, it has to be taken into consideration that the elastomers that are being used here are under a considerable load due to the high rotational speeds as a result of the high frequencies on the one hand and as a result of the continuous operational state on the other and they must therefore be replaced considerably more frequently whereby appropriate maintenance measures are necessary, and not just in a special case. In addition, this is a completely different situation from that of laboratory centrifuges or washing machines for instance, since these are only being used as and when necessary and in batch-like manner.
Moreover, it also has to be taken into consideration that the vibration damping elements in the vicinity of the centrifuge drum in the interior of the entire sugar centrifuge are now in a region which is exposed to very high temperatures since it is precisely here in the vicinity of the drum where the heating region is located in sugar centrifuges. As a result of this additional loading, the vibration damping elements which are frequently in the form of rubber buffers have to be additionally replaced on a still more frequent basis in order for them to be able to fulfil their proper function. Furthermore, there are high mechanical loads on the drive unit whereby vibrations of comparatively large amplitude occur between the drum axis and the motor.
It would be desirable co produce a vibration camping system for sugar centrifuges which is effective and maintenance-friendly at the same time.